Waveguides and methods of bending waveguides



Jan. 9, 1962 R. l. GILL WAVEGUIDES AND METHODS OF BENDING WAVEGUIDES Filed Nov. 28, 1958 then joining the two parts.

United States Patent 3,016,081 WAVEGUIDES AND METHODS OF BENDING WAVEGUIDES Ronald Irwine Gill, Harrow, England, assignor to The General Electric Company Limited, Kingsway, London, England Filed Nov. 23, 1958, Ser. No. 776,853 Claims priority, application Great Britain Dec. 2, 1957 6 Claims. (Cl. 153-32) The present invention relates to waveguides and methods of bending waveguides.

In some instances a waveguide is required having two bends which are adjacent one another but which are in ditferent planes. It has been suggested that .the difiiculties which arise in providing two such bends in a waveguide may be overcome by manufacturing the waveguide in two parts, each part including one bend, and Further difliculties then arise due to the necessity of ensuring that no irregularity or discontinuity occurs in the inside walls of the waveguide at the plane where the two parts are joined,

One object of the present invention is to provide an alternative method of manufacturing a Waveguide having two bends which are adjacent one another but which are in different planes.

In a method of bending a waveguide according to the present invention a mandrel is inserted from one end of the waveguide substantially to fill a first straight .part of the waveguide, said mandrel comprising a stack of substantially flat metal strips which have a width, at least over that part of their length which lies within the length of the waveguide which is to be bent, of slightly less than the dimension of the internal cross- 'section of the waveguide parallel to which the said strips guide which has a bend in it, the waveguide then being bent such that the plane containing all the longitudinal axes of the strips forming the mandrel is unaltered, the said mandrel and the said member or members then being removed.

The said strips may be formed of a resilient metal such as steel. Preferably said stack of strips is formed by a stack of strips which has been doubled back on itself, to donble the effective thickness of said original stack, and then clamped at a point adjacent the loop so formed.

Preferably said bend in the portion of the waveguide which has a bend in it and the bend which is formed by the present method are in different planes.

One method of manufacturinga waveguide with two adjacent bends in different planes, in accordance with the present invention, will now be described by way of example with reference to the accompanying drawing in which:

FIGURE 1 shows a partly cut-away perspective view of a waveguide which is to be bent by a method in accordance with they present invention, prior to such bending,

FIGURE 2 shows a side elevation of a part of a mandrel used in the method,

FIGURE 3 shows a perspective view of a first member used in the method, and

FIGURE 4 shows a perspective view of a second member used in the method.

The waveguide which it is required to bend is a length of waveguide formed of cartridge brass, that is to say,

3,016,081 Patented Jan. 9, 1962 an alloy of copper containing approximately 30% of 21110. approximately 0.4 inch by 0.9 inch. Prior to bending, the waveguide is cut to a length of say twelve inches, care being taken to ensure that the plane of the cut at each end of the length of waveguide is at right angles to the longitudinal axis of the waveguide. The waveguide is deburred and a small hole is drilled near one end for ease of handling during the subsequent heat treatments.

As the waveguide is normally too brittle to be satisfactorily cold worked it is annealed in an air circulating furnace. The furnace is brought to a temperature of 600 C. and a number of waveguides then loaded 7 in. The Waveguides are hung vertically, from the small hole previously mentioned, to minimise bowing at the elevated temperature. The temperature of the furnace is maintained steady at 600 C. for fifteen minutes and the waveguides are then quickly removed and quenched in water, this being followed by a dip in an acid bath to remove scale.

The present application is not concerned with overcoming the difiiculties of providing a waveguide with a first bend and consequently no description directed to the provision of this bend is included. A method in accordance with our co-pending British patent application No. 37541/57 may, however, conveniently be used. Hereinafter the initial bend providedin the waveguide will be referred to as the first bend. It is now required to provide the waveguide with a second bend adjacent the first bend but in a plane perpendicular to the plane of the first bend. v

Referring now to FIGURE 1 of the drawing, the waveguide 1 is first loaded with a mandrel 2, the mandrel 2 being loaded from the end of the waveguide 1 corresponding to the side of the first bend 3 on which the second bend is required. This mandrel is made up of a plurality of fiat strips 4 of spring steel, the strips 4 having substantially uniform cross-sections along their lengths except at their ends, where they are shaped as will be hereinafter described. The width of the strips 4 is some two to four thousandths of an inch less than the dimension of the internal cross-section of the waveguide 1 which is at right angles to a wall 5 of the waveguide 1, the plane of which is to be the same both before and after the waveguide lhas been given its second bend. The total thickness of the strips 4 making up the mandrel 2 is some one to two thousandths of an inch less than the other dimension of the internal cross-section of the waveguide 1.

The strips 4 forming the mandrel 2 are made up of two single strips 6 and 7 and a group of strips 8. The

group of strips 8 comprises a number of strips formed into a stack which is then doubled back on itself and held by means of a clamp 9 near the point where it has been bent. The stack of strips 8 thus has aloop 10 formed at one end and the loop 10 is arranged to lie around part of the circumference of a bobbin 11, which has a rectangular channel 12 around its circumference. The stack of strips 8 lie within the channel 512 and the clamp 9 is drawn up close to the bobbin 11 so that it is not able to fall outduring the subsequent operations.

The mandrel 2 and the waveguide 1 are lubricated with tallow and the mandrel 2 is then loaded in to the waveguide [as follows. The group of strips 8 is loaded The waveguide has an internal cross-section of shows a side elevation of one end of one of the strips 4, the .two inner ends 13 of the single strips 6 and 7 and the ends 13 of the strips 8 in the stack remote from the bobbin 11 are shaped to correspond with the shape of the internal Wall of the waveguide '11 on the outside of the first bend 3. The ends 13 of each of the strips 4 making up the mandrel are also provided with a notch 14 on the sides opposite this shaping.

The mandrel 2 is locked in position by means of two members now to be described. Referring to FIGURE 3 of the drawing, the first of these members 15 comprises a metallic rod 16 of rectangular cross-section, each dimension of its cross-section being less than either of the internal dimensions of the waveguide 11. At one end of the rod' 16 is provided a shoe 17 the shape of which corresponds to the shape of the internal wall of the waveguide 1 on the inside of the first bend 3.

Referring now to FIGURE 4 of the drawing, the member 18 comprises a bar 19 of metal the cross-section of which is substantially the same as the internal crosssection of the waveguide 1. In one face of the bar 19 is formed a longitudinal recess 22 the dimensions of which correspond to the dimensions of the rod 16 (FIG- URE 3). Projecting beyond one end of the bar 19 is a projection 23 which engages with the notches 14 in the ends of the strips 4 making up the mandrel 2.

Referring again to FIGURE 1 of the drawing, the two members 15 and 18 are loaded in sequence into the Waveguide 1 the member 15 being slid into the waveguide 1 first and the member 18 sliding in second and being arranged to engage with the notches 14 in the strips 4 of the mandrel 2. With the mandrel 2 and the two members 15 and 19 in position substantially the whole cross-section of the waveguide 1 which has been, or is to be, bent is filled and consequently supported.

The waveguide 1, complete with the mandrel 2 and the members 15 and 18 is then given the requiredsecond bend as indicated by the part 24 of the waveguide shown in broken lines. This may be done manually in a suitable jig or on a power turntable of known form. in either case adequate external supporting and clamping arrangements for the part of the waveguide 1 containing the first bend 3 are provided. There will naturally be some degree of spring-back of the waveguide 1 when the bending force is removed and it is therefore necessary to bend the waveguide 1 slightly more at this stage than is required in the final product, the amount of extra bending required being small and being found by trial.

The bent waveguide 1 is removed from the jig or turntabel and the two members 15 and 13 withdrawn first. The strips 8 are then Withdrawn on ahydraulically operated draw bench by means of a draw bar exerting a pull on a rod passed through an axial hole 25 in the bobbin 11. The single strips 6 and 7 may then be removed by hand.

If necessary the wave-guide 1 is then deburred and it is degreased prior to stress relieving in an air circulating furnace for a period of one hour at 250 C. to 270 C. After removal from the furnace the waveguide 1 is allowed to cool and air and is finally bright acid dipped.

It will be realised that the invention is equally applicable to waveguides formed of other metals, for example, aluminum, and that it may be used for a wide range of waveguide sizes and shapes of bend.

Iclaim:

1. A waveguide-bending mandrel for use in making a second bend in a waveguide adjacent a previouslymade first bend comprising a first part formed by a stack of substantially fiat metal strips, said stack including a group of strips which has been doubled back on itself and loosely held together adjacent the loop so formed, and a second part adapted to cooperate with the end of the stack of strips remote from said loop, the cooperating ends of said first and second parts of the mandrel being shaped so that, in use, they meet and interlock in the portion of the waveguide which has said first bend in it, the cross-section of the mandrel being such that, when it is in use, the portion of the waveguide which has said first bend in it and the portion in which the second bend is to be made is substantially filled.

2. A waveguide-bending mandrel according to claim 1 wherein said strips are formed of a resilient metal.

3. A Waveguide-bending mandrel according to claim 2 wherein said metal is steel.

4. A waveguide-bending mandrel according to claim 1 wherein at least those portions of the mandrel which, When the mandrel is in use, lie within said portion of the waveguide which has said first bend in it and Within said portion in which the second bend is to be made, are of rectangular cross-section.

5. A waveguide-bending mandrel according to claim 4 wherein said first part of the mandrel includes two additional strips similar to the strips forming said group of rips, said additional strips being arranged, when the mandrel is in use, to lie one between each of the outer strips of said groups of strips and the adjacent wall of the waveguide.

6. A method of bending a waveguide in a straight part of the waveguide adjacent a previously-made first bend which connects said straight part with another part, said method comprising the steps of providing a group of substantially flat metal strips, doubling said group of strips back on itself at a loop to provide a stack, loosely holding together the stack adjacent the loop, forming the end of the stack remote from the loop into an irregular shape that includes a portion which substantially matches the internal shape of the first bend and an irregularly shaped portion which faces into the other part of the Waveguide from the first bend, providing an element receivable in the other part of the waveguide, said element having an irregularly shaped end which matches the irregularly shaped portion of the stack, whereby said element and said irregularly shaped portion are interlockable in the waveguide adjacent the first bend, inserting the stack and element into the waveguide to substantially fill the same at and adjacent the first bend, bending the stack and the waveguide about an axis parallel to the planes and perpendicular to the lengths of the strips, and then removing the stack and element from the waveguide.

Fuchs et al. Apr. 21, 1959 

